What I do to create the master black, master grey and master white layers is use the channel mixer method detailed in the below tutorial. You can then use Darth_Brooks methods to set them as screen, multiply and overlay. As your chosen image has 3 different colours on the shirt, you will have to do this separately for each colour segment and this may prove difficult to match up exactly.
Oh my word. That makes it SO much easier. For the gray overlay layer, if you set the red output to 50 in each channel you get a neutral gray color.